Soft polyvinyl chloride (PVC) is widely used to produce articles like toys, footwear, profiles, instrument panel skins, furniture, sporting goods and the like. Soft PVC is PVC that contains one or more plasticizers, e.g., a phthalate. PVC is used in these applications for a number of reasons not the least of which are that it is paintable without a primer or other surface treatment, e.g., plasma or corona, and it imparts a Shore A hardness to the article of 50-95. As a frame of reference, a door seal typically has a Shore A hardness of about 55, an automotive tire tread of 50-70, and hydraulic O-rings of 70-90.
Interest exists in replacing the soft PVC in these applications with materials that are considered more environmentally friendly, e.g., free of halogen-containing polymer. Especially with respect to toys for small children, interest exists for substitutes for soft PVC that do not contain components, e.g., phthalate-based plasticizers, that will leach or otherwise migrate from the article under normal use conditions yet are paintable without the need for a primer or other surface treatment and will impart the desired Shore A hardness to the article.
Certain rubbers, e.g., styrene-butadiene-styrene (SBS) and styrene-ethylene/butylene-styrene (SEBS), and compositions containing these rubbers, can be painted without a primer or first receiving some other surface treatment by certain paints, e.g., acrylic-modified paint. These rubbers can also impart the desired Shore A hardness to the article, but the presence of leachable, small (e.g., typically less than 4 units in length) polymeric units derived from styrene monomer, e.g., dimers and trimers, in these rubbers disfavors their use in many applications, particularly toys.
Other rubbers, e.g., polyolefin elastomers such as ethylene-propylene (EP) and ethylene-propylene-diene monomer (EPDM), do not contain leachable, small polymeric units derived from styrene monomer but typically require a primer or other surface treatment for painting, This adds, of course, to the time and cost of producing such articles.